Binary Tree Zigzag Level Order Traversal

Given the root of a binary tree, return the **zigzag level order traversal** of its nodes' values (i.e., from left to right, then right to left for the next level and alternate between). Output all values in zigzag traversal order on a single line separated by spaces. ### Constraints - The number of nodes in the tree is in the range `[0, 2000]`. - `-1000 <= Node.val <= 1000` ### Input Format A single line containing space-separated integers representing the tree in level-order (-1 for null). ### Output Format Print the space-separated integers of the zigzag traversal.